The present invention relates in general to an apparatus and method for analyzing production fluids from a subterranean formation and, in particular, to an apparatus and method for determining the constituent composition of the produced fluids with a downhole fluid analyzing device that communicates correlating data to the well surface.
One aspect of reservoir management includes maximizing the daily production of hydrocarbons from a particular producing interval. When multiple zones are commingled in a single tubing string and the combined effluent from all of the zones is flowed to the surface, it is difficult to discriminate the contribution from each interval. Accordingly, it is desirable to gather and monitor the gross flowrate from each producing interval and to determine the constituent volumetric flowrates of oil, water and gas. Another aspect of reservoir management is maximizing the total recoverable reserves from the reservoir. This typically requires more detailed knowledge of the constituent rates from each interval which may be used to determine the most optimum flow regime. For example, such data can be used to select the optimum flowrates for each of the producing zones as well as the appropriate hydrocarbon to water ratios to, among other things, prevent coning.
In the past, one method of obtaining data relating to the constituents of production fluids from a particular producing interval was through sampling. This procedure typically required lowering wireline tools downhole after the production flow was ceased, isolating the zone of interest, reinitiating the fluid flow from that zone, obtaining the. production fluid sample, ceasing the flow and then retrieving the sample. This procedure would then be repeated for the other zones of interest. It has been found, however, that the costs associated with this procedure are high due to well downtime and the associated loss of production revenue.
Another method of obtaining fluid flow data has been through the use of permanent downhole gauges which obtain production fluid data without the need for shutting in production. Such permanently installed completion systems have incorporated multi-drop downhole data acquisition and control systems which include an array of downhole sensors spaced throughout a well. Such sensors have been used to monitor pressure and temperature characteristics. It has been found, however, that such sensors are relatively ineffective in identifying the constituent volumetric flowrates of the production fluids.
Therefore, a need has arisen for an apparatus and method that provide information relating to the daily production of hydrocarbons from a particular producing interval. A need has also arisen for such an apparatus and method that provide detailed information relating to the constituent rates from each interval. Additionally, a need has arisen for such an apparatus and method that provide this information without having to cease production.
The present invention disclosed herein comprises an apparatus and method that provide information relating to the daily production of hydrocarbons from a particular producing interval. Specifically, the apparatus and method of the present invention provide detailed information relating to the constituent rates from each interval. Using the apparatus and method of the present invention, this information is obtained without having to cease production.
The apparatus of the present invention comprises a vessel having an interior chamber that is in selective communication with a stream of fluids produced from a subterranean formation. A flow control device associated with the apparatus is used to selectively permit and prevent the produced fluid from entering and exiting the interior chamber.
For example, the flow control device may have an open position, wherein the produced fluid flows through the interior chamber of the apparatus and a closed position, wherein the produced fluid in the interior chamber is contained as a sample.
Once such a sample is obtained, the sample is allowed to separate within the interior chamber into its constituents using, for example, gravitational separation. In a typical sample of produced fluids, the constituents may include gas, oil and water. Due to the differences in the specific gravity of these constituents, the gas migrates to the top of the interior chamber and the water migrates to the bottom of the interior chamber with the oil positioned therebetween. As such, a gas/oil boundary forms between the gas and the oil. Likewise, an oil/water boundary forms between the oil and the water.
A gauge attached to the vessel is used to identify the location of these boundaries which allows for the determination of the constituent volumetrics of the produced fluid. The gauge may include an array of transmitter elements and an array of corresponding receiver elements that are disposed oppositely of one another on the vessel. Each of the transmitter elements transmits an energy wave through the sample of the produced fluid that is received by the corresponding receiver element. The receiver elements detect changes in the energy waves caused by the constituent of the sample of the produced fluid through which that energy wave propagated.
For example, if the energy waves propagated through the sample are light waves, the gas constituent will absorb a portion of the light energy, the oil constituent will be substantially opaque to the light energy and the water constituent will be substantially transparent to the light energy. As such, the locations of the gas/oil boundary and the oil/water boundary may be identified. Once the locations of the boundaries are identified, this information may be sent to a data acquisition system on the surface such that the constituent composition of the sample of the produced fluid may be calculated.
In the method of the present invention, the constituent composition of a produced fluid is determined by disposing a fluid analyzing device having an interior chamber downhole, selectively communicating the interior chamber with a stream of the produced fluid, collecting a sample of the produced fluid in the interior chamber, allowing the produced fluid to separate into constituents and identifying the level of an interface between the constituents with a gauge.